In the title poem of Taxing the Rain (1992), Penelope Shuttle wrote: "When I wake the rain's falling / and I think, as always, it's for the best, // I remember how much I love rain, / the weakest and strongest of us all; / as I listen to its yesses and no's, / I think of how many men and women / would, if they could, / against all sense and nature, // tax the rain for its privileges." Even as recently as the early 1990s this might have looked slightly whimsical to some, but Shuttle's prophecy of the death-wish of monetisation and environmental vandalism is nowadays everywhere confirmed, while her level, reasonable voice seems that of "sense and nature", commending life as a self-evident good against those who might claim to improve on it.

It is against this sturdy affirmation that Shuttle's work of recent years – Redgrove's Wife (2006), Sandgrain and Hourglass (2010), and the new collection, Unsent – must be measured, for these are books overwhelmingly about loss, following the death of Shuttle's husband, her fellow poet and frequent collaborator, Peter Redgrove. In "Our Little Books", one of many poems addressed to Redgrove, Shuttle touches on the continual intimacy of their literary relationship, where each left detailed marks on the other's work "till the poem untangled / and became itself.// You called then fascicles, / bundles of words, / poems in necessary transit / from work desk to world." The loss of Redgrove the man is also the loss of the fellow-writer, critic, adviser and listener, and the new poems in particular lament the necessity of speaking into the abiding silence where he used to be.

Some readers, this one included, will go a long way to prevent biography getting between them and the poems, as it tends to with Hughes and Plath, or Eliot and Vivienne Haigh-Wood, where critical inquiry sometimes gives way to gossip, which in turn makes the poetry into a mere pretext for curiosity. Shuttle and Redgrove are less well known, their relationship does not exhibit the X-certificate toxicity of the other couples, and both are poets first of praise and revelation – complementary spirits, with (very roughly) Shuttle's the airier voice and Redgrove's the more earthy: "we have often run away together / into the park of storms / where thunder and his sister lightning live". Their lives are properly part of the subject.

But these are lives greatly transmuted by imagination. For Shuttle and Redgrove, realism is almost a form of exotica. Where Redgrove's work clanks and steams with spectacular scientific-metaphysical machinery, Shuttle can evoke with the lightest of touches and a faith in the imagination's rightness. An early poem, "The Hell-Bender", describes a salamander: "He is a summer beast, / nimbly folding the water into shapes / that suit him, / his garments he might sleep or hunt in./ All feebler things are his serfs, his fodder."

This mixes the seemingly casual and the ceremonious issues in a kind of witty satisfaction stretching back via Bishop and Marianne Moore to the Old Testament. Alongside this is a mystical strain that seems peculiarly English, seeking to "describe / the mastery of flowers / grazing the earth // like translations done / without dictionaries". There is a wild, slightly mad humour, too. "Things You Can't Post", suggested by a Royal Mail leaflet, takes the list poem to the point of derangement: "You can't post Pathogens in Hazard Group Four, / museum corridors or false alibis, / air pockets, or the essence of Zen / or a comet or a moonbeam or a huge mirror / intended to be sent up into the sky / to reflect sunlight on the winter cities of Russia, // or filth."

"Thief", from Adventures with My Horse (1988), is a strange and, again, prophetic poem, ambiguously describing the shadow who stalks all endeavour and ordinary happiness, but inviting us to consider his thefts as a challenge of the kind involved in making art: "Each morning you open your eyes jealous as hunger, you walk / serpent-necked and dwarf-legged. In the thief's distorting mirrors, / you go nakedly through the sky's moonless gardens and pagodas / of envy that he gives you, the thief's gift, your seeding wilderness."

In the event, Shuttle's most recent work, where she looks squarely at loss, is often much barer: "eagle plus liver plus Prometheus plus Zeus: / you do the maths". Shuttle catalogues her husband's vast book collection – "so many only God / has time to read them all" – for sale, "having no more use for them, / not caring to interpret them alone". Yet "On the Other Hand" concludes: "I live mostly without care, // you know? // the way a solid autumn hour / carries all care within her fist."

This austerity is a way to challenge a loss that might otherwise be unanswerable: "the standing stone of time / says to me – / get a life, girlfriend" now that the "empty world tells me / we've heard enough about your sorrow, missy". The artfulness is in the exposure itself, the bare stage, the bereavement not over but the imagination still drawn to the impersonal fact of beauty, "as the full-leaf trees / buck their great green manes / in the strong westerly // and the field shines / in a sudden bright elegy / of sunlight".